The present invention relates to a method and a system for error correction of user information received via a communication network.
Document D1 U.S. Pat. No. 5,699,405 describes how data and voice signals of a communications information signal of a cellular radio telephone are decoded simultaneously by two decoders. A data signal of the information signal is decoded by a data decoder, and then a data signal sensor decides whether the decoded signal is a normal data signal. Only a normal signal is forwarded to a signal converter for executing a code conversion. The resultant signal is output by a transmitter circuit. A voice signal of the information signal is decoded by a voice decoder, and then a voice signal sensor decides whether the decoded signal is a normal voice signal. Only a normal signal is sent to a digital/analog converter for transforming into an analog voice signal. The validity of the decoded signals is verified, for example, by varying the frequency band and/or the amplitude of the decoded signals. Due to the simultaneous decoder operations, the data and the voice signals are decoded efficiently at high speed by one modem card. As such, there is one modem card for a cellular radio telephone for simultaneous transmission of data signals and voice signals to an information terminal, where an information terminal may be a computer.
In cellular text telephony, a cascade of a cellular radio receiver (e.g., GSM modem) and a CTM receiver (Cellular Text telephone Modem) is provided for received texts. An example of this is the U.S. American text telephony standard (see 3GPP TS 26.226) wherein text is first converted into audio signals by digital coding of an alphabet, channel coding and frequency modulation, and then the audio signals are processed further in the same way as normal speech by cellular radio terminals (cellular radio modems) and transmitted via a cellular radio channel. In order to guarantee the reliable transmission of emergency calls, maximum error rates are specified for the transmission of the individual letters (see 3GPP TS 26.231). A CTM receiver and a cellular radio receiver are not highly compatible, however, and the complete system (cellular radio+CTM) cannot achieve sufficiently good performance, particularly in the sense of transmission efficiency, for the following reasons:                A cellular radio voice coder/decoder (such as the AMR) in cellular radio is optimized for coding/decoding of human speech. For the artificially generated (CTM) audio signals, the voice coder/decoder is not efficient.        
Under poor channel conditions, the error concealment, which is optimized for the human ear, is no longer satisfactory for the transmission of text information.
Accordingly, the present invention is directed toward a method and a device in a communication network that will better satisfy requirements in the transmission of data containing user information.